1. Technical Field
The present invention relates to a technology regarding a seat belt retractor that withdrawably retracts a seat belt, and more specifically, it relates to a technology regarding a seat belt retractor including an energy absorbing member (EA member), such as a torsion bar, for limiting the load imposed on the seat belt by absorbing inertial energy (kinetic energy) of an occupant in case of emergency (i.e., when the seat belt is worn and sudden deceleration of the vehicle, such as caused by a collision, occurs) and a seat belt system including the seat belt retractor.
2. Background Art
Hitherto, a seat belt system provided in a vehicle, such as a motor vehicle, restrains the occupant by a seat belt in case of emergency as described above. In general, such a seat belt system includes a seat belt retractor that retracts the seat belt. In the seat belt retractor, the seat belt is retracted around a spool if the seat belt is not worn. When the seat belt is worn, the seat belt is withdrawn and is placed about an occupant. In case of emergency as described above, a lock mechanism of the seat belt retractor is activated so as to prevent the rotation of the spool in a direction in which the belt is withdrawn. Thus, withdrawal of the seat belt is prevented. In this manner, in case of emergency, the occupant is restrained by the seat belt.
In general, a seat belt retractor of an existing seat belt system limits the load imposed on the seat belt by absorbing the inertial energy of the occupant using an EA member. Some existing seat belt retractors limit the load imposed on the seat belt by effectively absorbing the inertial energy of the occupant through an energy absorbing operation (EA operation) caused by torsional deformation of a torsion bar serving as a first EA member and the energy absorbing operation (EA operation) caused by deformation of an EA plate serving as a second EA member (refer to, for example, PTL 1).
As illustrated in FIG. 6, in the seat belt retractor described in PTL 1, a shaft portion c of a locking base b of a lock mechanism a is inserted into and is disposed in a hole f extending in an axis direction of a spool e that retracts a seat belt d. In such a case, the shaft portion c of the locking base b is supported by the spool e via a ring member g.
In addition, a torsion bar h and an EA plate (not illustrated in FIG. 6) are disposed between the locking base b and the spool e. At a normal time, the locking base b and the spool e rotate in unison. In case of emergency, a lock portion b1 of the locking base b is locked by a pawl (not illustrated), and the rotation of the locking base b is stopped. Thus, the spool e rotates relative to the locking base b in a direction in which the seat belt is withdrawn. The relative rotation between the spool e and the locking base b causes torsional deformation of the torsion bar h. In this manner, a first EA operation that absorbs the inertial energy of the occupant is performed. Furthermore, the EA plate deforms and, therefore, a second EA operation that absorbs the inertial energy of the occupant is performed. As a result, the load imposed on the seat belt d that restrains the occupant in case of emergency can be limited.